The present invention deals with static underground structures that drain fluid or gas that is present at the exterior of a foundation or footing. More particularly, the field of the present invention involves the use of a porous medium that is either adjacent to the outside of a foundation or footing or part of a foundation or footing.
The terms foundation and footing are used interchangeably herein to indicate a conventional structure (usually entirely underground) intended to be used to support vertical loads including floors and walls. Footings are customarily relatively wide, so as to maintain reasonable pressures on the underlining ground.
The term mat (or drainage mat) is used herein as equivalent to an alternate type of subsoil drain pipe (conduit) that is formed of a biodegradable resistant plastic back with a dimpled core that is faced with a biodegradable resistant filter fabric that is porous to water, but not soil particles. Such conduits are made by manufactures including JDR Enterprises; Alpharetta, Ga. under trade names that include xe2x80x9cJ-DRainxe2x80x9d and by American Wick Drain Corporation; Monroe, N.C. under trade names that include xe2x80x9cAKWADRAIN.xe2x80x9d It is conventional to refer to the filter fabric as a geotextile and to form the filter fabric by techniques that include perforation of a film of biodegradable resistant plastic. It is known to make the filter fabric from plastics that include polypropylene, and to make the back and core from plastics that include polystyrene and polyvinyl chloride. U.S. Pat. Nos. 4,572,700, 4,923,331, and 4,943,185 include descriptions of conduits of the type encompassed by the term mat as used herein, and those patents are incorporated herein by reference. It is known to wrap filter fabric all of the way around the mat.
The major problem to be solved is the reduction of, or the elimination of, the detrimental effects of ground water in the vicinity of footings. Solutions to this major problem lower the water level in the vicinity of the footings.
In most locations, underground structures, such as footings, are subject to hydrostatic pressure from ground water. (Surface water will cause pressures when flooding is present.) A high water level outside of a footing causes an unbalanced pressure acting sideways against the footing. If the water level gets high enough, an unbalanced pressure acting sideways can be exerted on the wall supported by the footing. Footings and supported walls are not usually designed for such pressures, and eventually water will seep into the building through the almost inevitable cracks or joints. While coatings on the outside can reduce the water intrusion, it is usually not economical in residential buildings to design the footings and walls safely to withstand hydrostatically produced side pressures.
The traditional way to relieve hydrostatic pressure is to install a drain around, and close to, the footing. Various materials capable of communicating water are used to form the drains including perforated drain pipe (tile) under and adjacent to a layer of aggregate (such as small stones) that serves to reduce the rate of infiltration of the finer soil, which tends to clog the pipe""s perforations.
The traditional practice is to cast the footing with concrete placed between form walls. A trench or hole wider than the eventual footing is dug around the perimeter of the site. Within the trench a form is constructed of an opposing pair of flat, abutting, vertical panels, or boards, made of wood, plastic, metal, or the like, so as to form a continuous channel to receive concrete. The opposing panels are spaced apart (usually by a constant distance) with their flat insides facing the channel and their outsides braced with stakes or the like. To communicate water from outside of the eventual footing to a sump, or the like, that is inside of the footings, sections of four inch pipe are placed on the bottom inside of the form, from one side of the form to the opposite side of the form, about every 25 feet (or as required by code). These periodically placed sections of pipe need to be protected from the ingress of concrete while the concrete is soft and will serve as through-conduits when the forms are removed. Concrete slurry is poured within the channel, leveled, and allowed to cure. After the concrete has cured, the forms are removed, drain pipe and aggregate (as aforementioned) are placed just outside of the footing, connection of the drain pipe to a sump (or the like) is effected (often through the aforementioned through-conduits), and the trench is backfilled. Placing drain pipe and aggregate often must be preceded by a labor intensive clearing of accumulated debris from the trench and the providing of an appropriate bed for the drain pipe. The traditional practice has evolved to include placing a fabric sock around the perforated drain pipe. The sock serves as a sieve to attenuate the ingress of soil particles into the perforated drain pipe while readily passing water. The traditional method just described may fairly be described as conventional.
Effecting a sound, long-lasting system of drainage using the described, conventional system requires significant workmanship. Opportunities for drain pipe to become dislodged or crushed are inherent in the traditional method described. The objectives of the present invention include overcoming the problems of the traditional method and its resultant system. As will be seen, the present invention may be carried out with workmen of little skill, and the system is inherently robust and resistant to damage.
In recent years, another method to relieve part of the hydrostatic pressure has found some favor. Herein, this method is called the horseshoe method. The horseshoe method begins after a foundation (including a set of through-conduits) and the wall the foundation supports have been constructed. Using an adhesive, or some other form of attachment, a mat is attached near the junction of the footing and the wall the footing supports after the wall and footing have been formed. The mat so placed must be periodically connected to a conduit or pipe extending away from the footing. That pipe (called a horseshoe conduit because of its appearance) connects to the mat and then curves down to connect to one of the aforementioned through-conduits. A horseshoe conduit is easily damaged during backfilling and operations near a horseshoe conduit. A horseshoe conduit is associated with each through-conduit and each horseshoe conduit must be water tight.
In addition to the susceptibility of damage to the horseshoe conduits during construction, the technique of using a mat near the junction of the footing and the wall the footing supports has additional issues. Since ground water is only removed from near the top of the footing, hydrostatic pressure on the footing (and on each horseshoe conduit) has not been significantly reduced. Damage to the footing could result and any breach of a horseshoe conduit (which are under pressure) will include damaging ingress of soil into the drainage system.
Whether the traditional method or the horseshoe method is used to effect a drainage system, such drains"" through-conduits are connected to a sump, or the equivalent, so that gravity, or a pump, tends to take water away from the footing. The present invention includes a novel way to solve the stated major problem of the reduction of, or the elimination of, the detrimental effects of ground water in the vicinity of footings.
Improvements to the old traditional technique of foundation drainage described previously have long been sought. U.S. Pat. No. 3,613,323 to Hreha shows an early use of a perforated conduit (duct) placed on the outside of, and part of, a footing""s form. A similar incorporation of a perforated conduit into the outside of a foundation""s form is found in U.S. Pat. No. 5,120,162 to Parker, U.S. Pat. No. 5,399,050 to Jacobus, and U.S. Pat. No. 5,406,785 to Baum. In addition to the presence of a perforated conduit attached to, and on the outside of, a form wall, these devices include an expectation of at least the outside form wall and its conduit being permanent. Advantageously, at least one of the form walls does not have to be removed after concrete sets. Disadvantageously, while there might be a labor savings from not having to remove the permanent form wall, the permanent form wall is expected to be rather complex and expensive to manufacture, and to involve additional labor and expense to erect as compared to the old technique. The resulting drainage conduit will be in front of the resulting foundation and thus subject to all of the hazards attendant to the drainage tile of the older systems of drainage. A net advantage to these systems is not apparent and these systems have not found much favor in the marketplace.
A need remains for a foundation drainage system that minimizes the total capital and labor cost attendant to the total implementation of the drainage system, while producing a system that is inherently long lasting and likely not to be damaged by the hazards attendant to construction. The objectives of the present invention include satisfying these, and other, needs.
The present invention is a novel process of using mostly existing materials to effect an efficient and relatively inexpensive footing drainage system, and the apparatus that results from the use of that process. The process starts after the form for a footing is erected.
A mat (as previously described) is placed vertically inside of the empty form and with the mat""s porous side against the inside of the outside wall of the form. The mat is extended horizontally along the entire length of the inside of the form being periodically spliced with suitable tape, or an equivalent. The bottom edge of the mat rests on the bottom of the form. Should drainage wish to be effected on the inside of a footing, a similar band of mat may be placed against the inside of the inside wall of the form.
Periodically, a T makes a fluid connection between the mat and a through-conduit that extends across the form to an attachment on the opposite form wall. When the form is removed after concrete is poured and cured, the T and through-conduit effect the way for water in the mat to pass to a sump, or the like, that is within the foundation.
Concrete is poured between the form walls and the concrete is leveled. With a small amount of care, it is easy to ensure that while pouring the concrete the concrete presses the mat against a form wall and that no concrete is between the mat and a form wall. The concrete level (height) is expected to be above (taller than) the mat and thus when the concrete cures a protective eyebrow of concrete will be formed above the mat. The presence of an eyebrow of concrete impedes causing damage to the mat after the forms are removed. A person working within the trench after the form is removed cannot step on the mat. The mat is also protected from backfilling of the trench, which takes place after the forms have been removed.
When the concrete has cured, the forms are removed. A conventional drainage system is connected to the now exposed openings to through-conduits (openings appear on the inside of the footing), and, when the trench adjacent to the now exposed fabric side of the mat (the fabric side of the mat appears on the outside of the footing and is essentially flush with the outside face of the footing) is cleared, one may place aggregate fill adjacent to the fabric. However, it has been found that the present invention functions satisfactorily, and preferably, without aggregate fill adjacent to the mat. The remainder of the trench is then backfilled and work progresses to the construction of structures to be supported by the well-drained footing.